In the case where an earthquake having a relatively long period occurs or at the time of strong wind, a building continues to shake for a long period of time at a low (first-order) natural frequency. Usually, if the vibration of building exceeds a vibration level set by a seismic sensor, the operation of elevator transfers to a control operation. In this control operation, the running elevator is stopped at the nearest floor to prevent passengers from being trapped in the car.
On the other hand, in the shaft of elevator, long objects such as a main rope for driving the elevator, a compensating rope, a governor rope, and traveling cable are provided, and each rope is transversely vibrated by the shake of building. In particular, if the natural frequency of the transverse vibration of rope coincides with the natural frequency of building and resonances occur, the shake amount of rope increases with time, so that the equipment in the elevator shaft may be damaged by the contact of rope with the equipment, the rope may be caught by something, or other troubles may occur.
Since the natural frequency of the transverse vibration of rope depends on the tension of the rope and the rope length determined by the position of a car, it is necessary to properly select the stop position of the car to prevent the resonance of the transverse vibration of the rope with the shake of building.
As an elevator operation control device at the earthquake time, a device has conventionally been known in which if preliminary tremors of earthquake are detected, it is judged whether the car is located above or below the intermediate floor of the building, and if the car is located above the intermediate floor of the building, the car is moved to the intermediate floor and stopped there, and if the car is located below the intermediate floor of the building, the car is stopped at the nearest floor and then is moved to the intermediate floor and stopped there (for example, refer to Patent Document 1).
Also, as another conventional art, for some elevator operation control devices, the car is stopped at a position at which the main rope does not resonate (non-resonance position) (for example, refer to Patent Document 2).
Patent Document 1: Japanese Patent Laid-Open No. 57-27878
Patent Document 2: Japanese Patent Laid-Open No. 56-82779